// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
#define BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_

#include "base/location.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/single_thread_task_runner.h"

namespace base {

// RefCountedDeleteOnMessageLoop is similar to RefCountedThreadSafe, and ensures
// that the object will be deleted on a specified message loop.
//
// Sample usage:
// class Foo : public RefCountedDeleteOnMessageLoop<Foo> {
//
//   Foo(scoped_refptr<SingleThreadTaskRunner> loop)
//       : RefCountedDeleteOnMessageLoop<Foo>(std::move(loop)) {}
//   ...
//  private:
//   friend class RefCountedDeleteOnMessageLoop<Foo>;
//   friend class DeleteHelper<Foo>;
//
//   ~Foo();
// };

// TODO(skyostil): Rename this to RefCountedDeleteOnTaskRunner.
template <class T>
class RefCountedDeleteOnMessageLoop : public subtle::RefCountedThreadSafeBase {
public:
    // This constructor will accept a MessageL00pProxy object, but new code should
    // prefer a SingleThreadTaskRunner. A SingleThreadTaskRunner for the
    // MessageLoop on the current thread can be acquired by calling
    // MessageLoop::current()->task_runner().
    RefCountedDeleteOnMessageLoop(
        scoped_refptr<SingleThreadTaskRunner> task_runner)
        : task_runner_(std::move(task_runner))
    {
        DCHECK(task_runner_);
    }

    void AddRef() const
    {
        subtle::RefCountedThreadSafeBase::AddRef();
    }

    void Release() const
    {
        if (subtle::RefCountedThreadSafeBase::Release())
            DestructOnMessageLoop();
    }

protected:
    friend class DeleteHelper<RefCountedDeleteOnMessageLoop>;
    ~RefCountedDeleteOnMessageLoop() { }

    void DestructOnMessageLoop() const
    {
        const T* t = static_cast<const T*>(this);
        if (task_runner_->BelongsToCurrentThread())
            delete t;
        else
            task_runner_->DeleteSoon(FROM_HERE, t);
    }

    scoped_refptr<SingleThreadTaskRunner> task_runner_;

private:
    DISALLOW_COPY_AND_ASSIGN(RefCountedDeleteOnMessageLoop);
};

} // namespace base

#endif // BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
